1.0 Field of the Invention
The present invention is directed to pump and grinder assemblies and, more particularly, to a pump and grinder assembly for use with a steam producing device, with the pump and grinder assembly being effective for pumping scale out of the steam producing device and grinding the scale into relatively smaller pieces.
2.0 Related Art
Steam producing devices such as steam generators, boilers, coffee makers and others, are well known in the art. Steam generators, which are vented to atmosphere, and boilers, which are pressurized to various gauge pressures, have a variety of applications including multiple applications in the cooking industry. For instance, steam generators and boilers are commonly used with convection-type steamer ovens such as those used in restaurants and other commercial establishments. The water supplied to these steam producing devices typically contains various minerals such as calcium, sodium, iron and magnesium. When the water is heated to its boiling temperature, the molecular bonds of the water break down causing these minerals to be deposited upon various interior surfaces of the housing of the steam producing device and components, such as water level sensors, disposed at least partially within the steam producing device. The minerals are typically deposited on any surface which is exposed to boiling water or steam, which constitutes essentially all interior surfaces of steam generators and boilers. The mineral deposits are referred to herein generically as xe2x80x9cscalexe2x80x9d. The buildup of scale within the steam producing device has a variety of adverse effects including increased operating costs and possible failure of the steam producing device.
Gas-fired steam producing devices typically include an outer housing and a firetube assembly contained within the outer housing. During operation, water is disposed in the space between the outer housing and the firetube assembly. Buildup of scale on the exterior walls of the firetube assembly reduces the thermal efficiency of the steam producing device, and therefore increases operating costs, by reducing the heat transfer from the metal walls of the firetube assembly to the surrounding water. The walls of the firetube assembly are heated by hot gas flowing within the assembly. The reduction in heat transfer through the water results in longer cooking times, with regard to steam producing devices used in the cooking industry, which is not desirable. The thermal efficiency of electrically-heated units is reduced when scale accumulates on the electrical resistance heating rods which are disposed within the water contained within the outer housing of the steam producing device and are used to transfer heat to the water.
Another problem with scale build up of this type is that it may lead to distortion or failure of the firetube assembly, which is typically made of stainless steel. This may occur as follows. The scale may accumulate on the exterior surfaces of the firetube assembly unevenly, with the thickness of the scale varying from top to bottom of the firetube assembly. Typically, the scale thickness increases with the temperature of the surface. The walls of the firetube assembly are generally hotter near the bottom where the gas burners are typically located, and are cooler near the top since the xe2x80x9chot airxe2x80x9d cools down, due to heat transfer, as it flows through the firetube assembly from bottom to top, typically through a tortuous flowpath. Locally thicker areas of scale build up create xe2x80x9chot spotsxe2x80x9d in the metal walls of the firetube assembly. As an example, an average local metal temperature may be about 300xc2x0 F., with a gas flame temperature of about 1000xc2x0 F. under normal circumstances. As a result of scale build up, less heat is transferred to the surrounding water, so that the local metal temperature rises significantly, such as to about 700xc2x0 F. by way of example. This may cause the wall of the firetube assembly to distort locally. Also, as one skilled in the art may appreciate, the presence of multiple hot spots may cause the metal wall of the firetube assembly to move to the extent that various seam or spot welds are pulled apart causing expensive repair or replacement of the unit. For instance, the spot welds attaching various interior heat transfer baffles to the walls of the firetube assembly may fail, causing water leaks into the combustion chamber of the firetube assembly. Additionally, the welds which attach the firetube assembly to the outer housing of the steam producing device may fail, which may result in water leaking externally of the steam producing device.
Operational costs may also be increased due to scale buildup on the water level sensors. When this occurs to the extent that the sensors are xe2x80x9climed overxe2x80x9d, the sensors malfunction and are no longer able to detect the water level within the steam producing device. Typically, these sensors are part of a control circuit used to control water fill valves and the operation of the gas burners or electrical resistance heating elements within the steam producing device. Accordingly, when this occurs it may be necessary to shutdown and xe2x80x9cde-limexe2x80x9d the device, which has been the industry standard for de-scaling water level sensors and attempting to de-scale the heat transfer surfaces within the steam producing device. A xe2x80x9cde-limingxe2x80x9d procedure is typically completed by pouring a chemical solution into the device, mixing it with water and running a cleaning cycle which adds to operating costs. The de-liming procedure may require the assistance of a service repairman or technician which further adds to operating costs.
Although de-liming procedures may be effective for cleaning the water level sensors and recovering thermal efficiency, by de-scaling various heat transfer surfaces such as the outer surfaces of the walls of a firetube assembly, other problems are created. During de-liming, pieces of scale, which may also be referred to as chips or chunks and vary in size and shape, are released and drop to the bottom of the steam producing device where they accumulate. Pieces of scale may also fall off during normal operation or during water filling and draining operations. When wet, these pieces tend to bond to one another forming a large mass of scale particles. When dry, the mass of scale particles is hard and brittle. Repeated de-liming procedures causes the accumulated mass of scale to grow in size which reduces the steam-generating capacity of the device due to reduced internal volume available for containing water. This also increases operating costs. Such an accumulation of scale may adversely affect water circulation within the steam producing device. As one skilled in the art may appreciate, when water boils, the water tends to rotate en masse, which mixes relatively hotter water with relatively cooler water within the steam producing device. However, the presence of significant scale build up within the unit may interrupt this natural convective flow of water, thereby reducing the efficiency of the unit.
Additionally, the buildup of scale in the bottom of the steam producing device may clog the drain system associated with the device. Steam producing devices such as a steam generator typically have a drain port extending through the housing of the device, which may be about two inches in diameter. However, a downstream drain valve, which is connected to the drain port by appropriate plumbing, may be much smaller, such as one-half inch diameter, due to cost considerations. Operators usually prefer remotely operated drain valves, such as electrically operated solenoid valves and, as known in the art, the price of these valves increases significantly with an increase in effective flow area. For instance, a nominal one-half inch solenoid valve may presently cost under one hundred dollars, whereas a nominal two inch solenoid valve may cost several hundred dollars. As may be appreciated, the presence of loose scale within the steam producing device may result in a relatively smaller flow area drain valve and associated plumbing becoming clogged before a relatively larger flow area drain port which may exist in the housing of the steam producing device. When the device drain is plugged, a potentially significant buildup of scale may result. This may lead to the various problems discussed previously.
Also, in extreme instances, the mass of accumulated scale may become so large that housing seam welds are broken or a xe2x80x9cdry firexe2x80x9d may occur within the steam producing device causing the device to be replaced. The term xe2x80x9cdry firexe2x80x9d, as known in the art, refers to the condition when the gas burners or electrical resistance heating rods of the steam producing device are turned on when there is no water contained within the steam producing device, as a result of the volume available to contain water being substantially filled with the scale.
In view of the foregoing disadvantages associated with known steam producing devices, a need exists for a cost efficient way to de-scale steam producing devices, without the intervention of a service technician or repairman.
In view of the foregoing needs, the present invention is directed to a pump and grinder assembly for use with a wide variety of steam producing devices, including, but not limited to steam generators and boilers used in the cooking industry, with the pump and grinder assembly being operatively effective for pumping water and loose scale contained within the water out of the steam producing device and grinding the scale into relatively smaller pieces which may be discharged out of the drain port of the pump and grinder assembly. The present invention is also directed to the associated methodology and, in one aspect, a combination of the pump and grinder assembly and a steam producing device. Use of the pump and grinder assembly of the present invention permits significantly reduced operating costs, relatively to those associated with known steam producing devices which are not used in combination with the pump and grinder assembly of the present invention, as well as decreased capital costs.
Operating costs are reduced as a result of use of the pump and grinder assembly of the present invention for a variety of reasons. In the first instance, thermal efficiency of the associated steam producing device is increased due to the periodic extraction of loose scale from within the housing of the steam producing device. Scale may be released during filling, draining or de-liming operations or during normal operation of the unit. The pump and grinder assembly includes a blade assembly which is in fluid flow communication with a water chamber defined by the housing of the steam producing device. Preferably, the blade assembly is rotated during each of the filling, draining and de-liming operations. This causes water, and any loose scale suspended within the water, to be pumped out of the housing of the steam producing device into a grinding chamber of the pump and grinder assembly, where the scale is ground into relatively smaller pieces by the blade assembly, and then discharged out of a drain port of the pump and grinder assembly. Accordingly, the scale does not accumulate within the housing of the steam producing device as described previously with regard to those devices which are not used in connection with the pump and grinder assembly of the present invention. Consequently, thermal efficiency is improved due to improved heat transfer to the water within the housing of the steam producing device, which results in lower cooking times and reduced costs to the operator. Also, the use of the pump and grinder assembly of the present invention results in several additional advantages to the operator of the associated steam producing device. For instance, since there is not a significant accumulation of scale within the housing of a steam producing device, the natural convective flow of water within the housing may occur when the water starts to boil, thereby mixing the relatively hotter and cooler water and improving the overall efficiency of the steam producing device which reduces operating costs. The absence of a significant accumulation or buildup of scale in the bottom of the housing of the steam producing device also permits the nominal steam capacity of the steam producing device to be substantially maintained, which also reduces operating costs. Further, since the loose scale is ground into relatively smaller pieces, use of the pump and grinder assembly of the present invention permits the use of relatively smaller and less expensive, remotely operated main valves, which reduces overall capital costs.
Use of the pump and grinder assembly significantly reduces the possibility of local hot spots and dry fires due to the periodic extraction of scale from within the housing of the steam producing device. Accordingly, use of the pump and grinder assembly of the present invention results in reduced chances of failure of the steam producing device and therefore a longer service life and reduced capital costs associated with the steam producing device.
According to a first aspect of the present invention, a pump and grinder assembly is provided for use with a steam producing device having a housing defining a water chamber and an aperture formed in the housing and communicating with the water chamber. The pump and grinder assembly of the present invention may be used with a wide variety of steam producing devices including steam generators, boilers, coffee makers and others. The pump and grinder assembly is operatively effective for pumping water and scale contained within the water out of the steam producing device and grinding the scale into relatively smaller pieces with may be discharged out of a drain port of the pump and grinder assembly. The scale may comprise calcium carbonate, also known as lime, or other mineral-based compounds. According to one preferred embodiment, the pump and grinder assembly includes a motor having a rotatable output shaft and a pump and grinder shaft coupled to the output shaft of the motor for rotation therewith. The pump and grinder assembly also includes a blade assembly having a plurality of blades, with the blade assembly being secured to the pump and grinder shaft for rotation therewith. A housing is interconnected to a stationary portion of the motor, with the housing defining a grinding chamber. The plurality of blades is disposed within the grinding chamber. The drain port is formed in the housing and communicates with the grinding chamber. Additionally, the drain port is disposed downstream of the blades. The pump and grinder assembly is mountable on the steam producing device so that the grinding chamber communicates with the water chamber of the steam producing device, permitting water and scale contained within the water to be pumped out of the steam producing device into the grinding chamber and then subsequently discharged through the drain port.
The pump and grinder assembly may further include a motor mount bracket having a first end portion attached to the motor, and a second opposite end portion. The assembly may also include a seal disposed between, and in sealing engagement with, the second end portion of the motor mount bracket and the housing. The seal, motor mount bracket and housing are secured to one another and, preferably, are fastened to one another.
The pump and grinder assembly may also include a hollow connecting member which may be used to mount the pump and grinder assembly on the steam producing device. Accordingly, the hollow connecting member may have various configurations, depending upon the particular steam producing device on which the pump and grinder assembly is mounted. The hollow connecting member has a downstream, proximal end secured to the housing of the pump and grinder assembly and an upstream, distal end terminating in a mount flange. The mount flange has a plurality of mount holes formed therein, with the mount holes being effective for receiving fasteners to attach the pump and grinder assembly to the steam producing device. The mount flange also has a generally centrally disposed aperture formed therein, with the aperture of the mount flange being substantially aligned with the aperture or drain port formed in the housing of the steam producing device when the pump and grinder assembly is attached to the steam producing device. Accordingly, an interior portion of the hollow connecting member and the grinding chamber are in communication with the water chamber of the steam producing device. The motor preferably comprises an electric motor and even more preferably comprises an alternating current electric motor. However, the motor may also comprise a direct current electric motor.
In one embodiment, the blade assembly further includes a first blade-supporting portion and a second blade-supporting portion, with the first and second blade-supporting portions being secured to the pump and grinder shaft for rotation therewith. In this embodiment, the plurality of blades includes first and second pluralities of blades, with the first plurality of blades being integral with the first blade supporting-portion and the second plurality of blades being integral with the second blade-supporting portion. Preferably, the blades are made as a one piece construction with the corresponding blade-supporting portion.
The first blade-supporting portion is disposed forward, or upstream of the second blade-supporting portion. In one embodiment the first plurality of blades extend radially outwardly and forwardly or upstream from the first blade-supporting portion and the second plurality of blades extend radially outwardly and rearwardly, or downstream, from the second blade-supporting portion. However, it should be understood that a wide variety of blades are suitable for use in the pump and grinder assembly of the present invention, provided that they are effective for pumping water and loose scale contained in the water out of the steam producing device and then grinding the loose scale contained within the water into relatively smaller pieces. In this embodiment, the first plurality of blades comprises a pair of blades, each having a blade tip, with the blade tips being separated by a first distance. A lateral or transverse internal dimension of the downstream, proximal end of the hollow connecting member is preferably less than or equal to this first distance separating the pair of blade tips so that the scale does not bypass the blades as water and the included scale is pumped through the blade assembly. The downstream, proximal end of the hollow connecting member has a circular cross-section in one embodiment, with the lateral or transverse internal dimension of this portion of the hollow connecting member being an internal diameter.
The pump and grinder assembly may further include a gasket which is disposed between the mount flange of the connecting member and the steam producing device when the pump and grinder assembly is mounted to the steam producing device. The gasket has a plurality of mount holes equal in number to, and alignable with, the mount holes formed in the mount flange of the connecting member. The gasket also has a generally centrally disposed aperture which is substantially equal in size to the generally centrally disposed aperture formed in the mount flange of the connecting member.
In one preferred embodiment, the pump and grinder shaft includes a first substantially cylindrical portion having a first outside diameter, and a second substantially cylindrical portion having a second outside diameter. The first and second substantially cylindrical portions are integral with one another, with the second outside diameter being less than the first outside diameter. The blade assembly is secured to the first substantially cylindrical portion of the pump and grinder shaft at an end opposite the second, reduced diameter substantially cylindrical portion of the shaft. In this embodiment, the pump and grinder shaft further includes a threaded portion, having external threads, which is integral with the second substantially cylindrical portion at an end opposite the first, relatively larger diameter substantially cylindrical portion of the shaft. In this embodiment, the assembly further includes a hollow coupling having a first end portion with internal threads which are engaged with the threaded portion of the pump and grinder shaft. Additionally, a set screw is provided, which protrudes through a hole in the wall of the hollow coupling and engages the rotatable output shaft of the motor, whereby the hollow coupling and set screw combine to rotatably couple the pump and grinder shaft to the rotatable output shaft of the motor. In other embodiments, the rotatable output shaft of the motor may be threadedly engaged with the coupling, with the pump and grinder shaft being secured to the coupling via the set screw. Also, it is noted that a flexible coupling may be used within the scope of the present invention. As known in the art, a flexible coupling refers to a coupling which may be used to accommodate some misalignment between shafts being coupled, in this case the rotatable output shaft of the motor and the pump and grinder shaft.
In a preferred embodiment, a bearing is provided having a flange portion and a substantially cylindrical portion integral with the flange portion. The substantially cylindrical portion extends longitudinally through the second end portion of the motor mount bracket which is disposed away from the motor, and the flange portion of the bearing is disposed in contacting engagement with a first surface of this portion of the motor mount bracket, which faces away from the motor. An annular, elastomeric seal is disposed longitudinally between the first, relatively larger, substantially cylindrical portion of the pump and grinder shaft and the flange portion of the bearing. This seal is disposed in surrounding relationship with the second, relatively smaller, substantially cylindrical portion of the pump and grinder shaft. A combination of this seal and the gasket which is disposed in sealing engagement with the bearing and hollow coupling substantially prevent water from entering the chamber defined by the motor mount bracket.
According to a second aspect of the present invention, an assembly is provided which includes a steam producing device and a pump and grinder assembly mounted on the steam producing device. The pump and grinder assembly may include the various features of the previously discussed embodiments of the present invention. The steam producing device includes a housing defining a water chamber and a fill port formed in the housing and communicating with the water chamber such that the fill port is effective for receiving water therethrough. The steam producing device further includes a drain port formed in the housing and communicating with the water chamber, and a heating device disposed at least partially within the water chamber. The heating device is effective for transferring heat to the water contained within the water chamber during operation of the heating device. In one embodiment, the heating device includes one or more electrical resistance heating rods. In other embodiments, the steam producing device may be gas-fired, with the heating device including a gas manifold, gas burners and an associated firetube assembly disposed within the housing of the steam producing device. In this case, air is heated by the gas burners, with the air then flowing through the firetube assembly which results in heat being transferred through the metal walls of the firetube assembly to the water contained within the housing between an interior surface of the housing and the firetube assembly.
The pump and grinder assembly is operatively effective for pumping water and scale, which is loose and disposed or contained within the water, out of the housing of the steam producing device and grinding the scale into relatively smaller pieces. This scale is typically lying on a bottom of the housing of the steam producing device. Preferably, the fill port and a drain port of the steam producing device are longitudinally spaced apart. This relative positioning of the fill port and drain port assists in moving water and the included scale toward the pump and grinder assembly during periods when the blade assembly is rotated within the grinding chamber.
According to a third aspect of the present invention, a method is provided for extracting loose scale contained in water from within a water chamber of a steam producing device and processing the scale for draining. According to one preferred embodiment, the method comprises the steps of: pumping at least a portion of the water and the scale contained therein out of the water chamber of the steam producing device; and grinding at least some of the scale into relatively smaller pieces.
The method according to the present invention may further include the step of mounting a pump and grinder assembly to a housing of the steam producing device, with the housing defining the water chamber of the steam producing device, and the pump and grinder assembly including a grinding chamber and a plurality of rotatable blades disposed within the grinding chamber. The method may also include the step of providing communication between the water chamber of the steam producing device and the grinding chamber of the pump and grinder assembly. This permits water and loose scale contained within the water to be pumped from the water chamber to the grinding chamber. Additionally, at least one of the step of pumping and the step of grinding may include the step of rotating the plurality of rotatable blades disposed within the grinding chamber.